Disagreement between the US and European Union (EU) has dominated the second day of global trade talks in Hong Kong.
The US trade representative urged the EU to open its markets
The US has renewed calls for the EU to make extra concessions on agriculture, but the EU reiterates that farming is just one factor in the negotiations.
The EU's refusal to make more cuts to farm subsidies and tariffs is blamed by some for the impasse at the talks.
Yet other nations - notably African cotton producers - also blame the US.
US Trade Representative Rob Portman said on Wednesday that a new agreement on agriculture had to be central to any new global free trade deal being achieved, however tentatively, at the World Trade Organization meeting.
"I believe either we move forward or we risk moving backward toward protectionism that will stunt economic growth and harm the developing world most," he told the conference.
He said the conference should set a date for another summit "to keep the pressure on".
The EU's Trade Commissioner Peter Mandelson retorted that a "policy of brinkmanship and bidding up is standing in the way" of agreement being reached in Hong Kong.
"There is an insistence that we should be talking about agriculture, agriculture, and nothing but agriculture. Fine, let's engage on agriculture, but let's also engage across the board," he said.
"We need much, much more on the table," he said, calling for reciprocal proposals to free up trade in industrial goods and services to match the EU's existing offer on farm products.
"The round will be successful only if we can show what we gain for what we gave - and everyone must accept that political reality."
Aiming to remove the focus from agriculture, the EU has instead put forward proposals to aid all exports from the very poorest nations.
Mr Mandelson wants such countries to be able to export duty and quota free on all products, be they agricultural or manufactured.
The assistance that the US government continues to give its cotton farmers has angered African cotton producers at the Hong Kong summit.
One of them - Benin - has threatened to walk out if the US does not agree to reduce cotton subsidies.
"We reiterate our call not to accept any consensus that doesn't take the legitimate interests of African cotton farmers into account," said Samuel Amehou, trade ambassador for Benin.
Meanwhile, the bloc of poorest countries and the G20 grouping of middle-sized developing economies have joined together at Hong Kong to renew their call for deeper cuts in the subsidies paid to farmers in wealthy nations in the US, the EU and Japan.
The EU's hand on agriculture is being tied by its member states.
Led by France, a number of EU countries have warned that they could block any deal if Europe makes additional compromises on agriculture.
The six days of world trade talks began in Hong Kong on Tuesday amid violent clashes between police and protesters.
Protests continued on Wednesday morning when 20 militant South Korean farmers tried to break through police lines, before they were forced to retreat after a baton charge.
Mr Portman also announced on Wednesday that the US would give $2.7bn (£1.5bn) to developing countries under the so-called "aid-for-trade" scheme to help them strengthen their trading capabilities.
However, he said the money must accompany real progress in slashing trade barriers.